I've got a J-Body question, but that forum has turned into a desert, so I was hoping some of the vast mechanical knowledge available here could help me. My 2002 Ecotec Sunfire with 200k is losing a small amount of coolant based on my having to top off an inch or two in the reservoir/surge tank(this model doesn't have a radiator cap) every other week, but I can't find any sign of a leak. I left it idling for an hour with a sheet of cardboard underneath and nothing. I left the sheet there overnight, and nothing. Hose attachments are all tight and the engine is bone dry. No overheating issues and no suspicious exhaust. It runs perfectly fine.
Today I rented a cooling system pressure tester and my system won't hold pressure at all. Once I pressurize to 15 psi, the needle slowly begins falling and in a couple of minutes all pressure is gone. I couldn't see or hear any escaping fluid during the test. The bottom of my engine is bone dry, as is the radiator, all the hoses, and the connections on the pipe that goes from the thermostat to the back of the water pump. I don't smell or see coolant in the passenger compartment, and I pulled a cold oil sample from the drain plug and the oil looks perfectly normal.
I'm totally stymied.
Any ideas?